Saturday, August 26, 2017

In the study at hand, the cuffs were applied before, not during the exercise.

This is not the first and it's certainly not going to be the last SuppVersityarticle about blood flow restriction (BFR). In contrast to previous articles, today's blog post does yet not focus on the effects of acute blood flow restriction on performance or gains. Rather than that, it discusses a recent study from the University Hospital of Düsseldorf (Germany), the Göthe University in Frankfurt, and the German Sport University in Cologne which investigated the effects of so-called "ischemic preconditioning" (which could be described as pre-workout BFR) on muscle damage and pain in response to eccentric biceps curls.

As Franz, et al., the authors of the study that is about to be published in "Medicine & Science in Sports & Exercise", ischemic preconditioning (IPC) is known to reduce muscle damage induced by ischemia and reperfusion-injury (I/R-Injury) during surgery - in that case, however, we are talking about damage to organs like the heart (Walsh 2008; Takagi 2008; D'ascenzo 2012). The German scientists did yet simply assume that ...

[d]ue to similarities between the pathophysiological formation of I/R-injury and eccentric exercise-induced muscle damage (EIMD), as characterized by an intracellular accumulation of Ca2+, an increased production of reactive oxygen species and increased pro-inflammatory signaling, [...] IPC performed prior to eccentric exercise may also protect against EIMD [exercise induced muscle damage]" (Franz 2017).

To confirm or falsify this assumption Fritz et al. recruited nineteen untrained healthy men and had them perform a standardized exercise protocol consisting of bilateral biceps curls (3x10 repetitions at 80% of the concentric 1RM), during which the subjects were assisted on the concentric part of the exercise until they reached an elbow flexion of ~50°. To accommodate for the previously discussed high inter-personal variability in subjects' creatine kinase [~muscle damage] response to exercise, the authors matched their subjects to the preconditioning (IPC+ECC) and control (ECC) group based on their CK response to an identical 1-RM test all participants had to do before the actual experiment.

Hong et al. (2017) took a closer look at the acute protective effects of IPC, albeit in rodents and not in response to eccentric exercise but in response to prolonged reperfusion stress.

How do the protective effects come about? Even though the study at hand is the first to observe muscle-protective effects of ischemic preconditioning (IPC) in the upper limbs of human subjects, it's not the first to deal with IPC in a skeletal muscle oxidative stress scenario. Earlier this year, Hong et al. observed in rodents that IPC could prevent morphological alternations (including myofilament, cell membrane, cell matrix, nucleus, mitochondria, and sarcoplasmic reticulum damage) in skeletal muscle cells. The scientists from the Fudan University in Shanghai ascribe these benefits to an IPC-induced increase in neovascularization; and yes, that happened in response to only one IPC session. Personally, I'd yet speculate that this is rather a corollary effect that occurs in response to the release of HSP or other signaling protein.

In addition, the development of reversible muscle swelling was monitored by assessing the circumference of the dominant arm at the mid-portion of the upper arm, defined as 50% of the length between the acromion process and the lateral epicondyle of the humerus. Subjective pain intensity was recorded on a 100-mm visual analog score (VAS).

The swelling of the arm(s), on the other hand, did not differ significantly. Since the same goes the muscle contractility that was measured by tensiomyography it is, in the absence of data on the short-term effects on muscle recovery and potential long-term effects on gains, difficult to tell how much of an advantage the impressive reduction in markers of muscle damage actually is.

Figure 3: Future studies will have to show what the pain reduction is worth.

Bottom line: While the study at hand shows impressive reductions in the most commonly used marker of muscle damage, I want to remind you of my previously voiced concerns over the accuracy and practical relevance of creatine kinase measurements - especially in untrained individuals. If the exuberant increases in muscle CK (reference max = 491, actual value >24000 → ~49-fold elevated) were an accurate quantitative measure of muscle damage, the subjects in the study at hand would have had to be sent to the emergency room (learn more). Accordingly, we must be careful with the interpretation of the results.

With both CK and pain (see Figure 3) being reduced, we have good reason to believe that the ischemic preconditioning did reduce muscle damage. What we shouldn't do, though, is to assume that the reduction in CK mirrors the actual reduction in muscle damage was identical to the reduction in 24-72h creatine kinase levels of ~95%. In the absence of changes in the contractile properties of the muscles and without (a) data about short-term effects on muscle strength and (b) long-term effects on training induced adaptation in form of strength and size increases, we will need follow-up studies to (i) tell us what the real-world effects of IPC are (in terms of acute strength and long-term gains) and whether it (ii) will work just as well for trained athletes, in whom the creatine kinase response is reduced compared to rookies.

Before these studies have not been done and the safety of using BFR for ischemic pre-conditioning has been confirmed, I would not recommend using it in athletes and/or gymrats, though | Comment!

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